1. Field of the Invention
The present general inventive concept relates to an apparatus and method of measuring noise in video signals, and more particularly, to an apparatus and method of accurately measuring noise in video signals, regardless of the characteristics of the video signals.
2. Description of the Related Art
Noise in video signals typically causes a reduction in the quality of images in a video signal. In particular, the noise may degrade the image and also cause the images to deteriorate when encoding and decoding the video signal. To reduce the noise in the video signal, enhance image quality, and increase efficiency of encoding and decoding video signals, various technologies have been developed. In order to reduce the noise in the video signals, a noise measuring apparatus has to be provided to accurately measure the amount of noise. The amount of noise measured by the noise measuring apparatus is generally expressed as a variance or a standard deviation, which is equivalent to a square root of the variance.
FIG. 1 is a block diagram showing a conventional apparatus for measuring noise in video signals. As shown in FIG. 1, the noise measuring apparatus comprises an SAD calculator 1, an SAD comparator 3, an SAD counter 5, a comparator 7, and an incremental and decremental counter 9.
The SAD calculator 1 calculates a sum of absolute difference (SAD), that is, the sum of absolute difference between neighboring pixels in an input image. The SAD calculator 1 calculates the absolute difference between a pixel of a current input image and a pixel of a one-clock-delayed input image, and calculates the SAD value which is the sum total of the absolute differences being one-clock-delayed, two-clock-delayed, and three-clock-delayed. The SAD comparator 3 determines whether the SAD calculated by the SAD calculator 1 lies within a predetermined range. If the calculated SAD lies within the predetermined range (i.e., the SAD is between a lower limit A and an upper limit B), the SAD comparator 3 outputs a true value. If the calculated SAD lies outside the predetermined range, the SAD comparator 3 outputs a false value. If the output of the SAD comparator 3 is a true value, the SAD counter 5 is increased by a certain count. The SAD counter 5 is reset once per picture cycle (field or frame period). Accordingly, the SAD counter 5 counts the SADs within the predetermined range in every picture.
The comparator 7 compares the count of the SAD counter 5 with a predetermined value (NE), and if the count of the SAD counter 5 falls below the predetermined value in every picture, the count of the incremental and decremental counter 9 is increased. If the count of the SAD counter 5 exceeds the predetermined value, the count of the incremental and decremental counter 9 is decreased. The count of the incremental and decremental counter 9, which is increased and decreased according to the result of the comparator 7, is a noise measurement. The noise measurement is fed back to the SAD comparator 3 as a reference to determine whether the SAD is within a predetermined range. An example of the conventional apparatus for noise measurement as described above is disclosed in U.S. Pat. No. 5,657,401.
However, since the noise measurements calculated by the conventional noise measuring apparatus depend on the distribution of the SADs of the video signals, the noise measurements may differ depending on the characteristics of the video signals. The noise measurements, in some cases, may even differ if the amounts of noise in the video signals are the same. For example, this may occur when comparing a noise measurement of a video signal containing complicated and detailed areas with a noise measurement of a video signal containing simple and plane areas. Accordingly, there is a need for an apparatus that is capable of calculating accurate noise measurements regardless of the characteristics of the video signals.